1. Technical Field of the Invention
The present invention relates to voltage regulation, and particularly to a circuit and method for making available within a system a current at a regulated voltage.
2. Description of the Related Art
It is known for some electronics-based systems to include a backup battery. In such systems, the battery backup is utilized for providing power to circuits in the system when the main power supply fails to exceed a minimum operating supply voltage level. By providing the backup battery in this way, information stored in the system in a volatile manner may be maintained without experiencing data corruption. In order to prolong battery life, the current drawn by some systems is substantially reduced relative to the current drawn during a normal mode of operation.
Typically, systems having two power supplies, such as a system having both a main power supply for normal operation as well as a backup battery, are connected to each power supply by a distinct transistor or group of transistors. Each transistor is activated depending upon whether the corresponding power supply is to be connected and provide power to the system circuits. In a system having a backup battery, the transistor associated with the main power supply may be quite large depending upon the amount of current that may be drawn by the system circuits.
Voltage regulators are known for receiving a supply voltage at a first level and providing at an output a supply voltage that is stepped-down from or less than the first level. It is difficult to design a voltage regulator for systems having multiple power supplies, because voltage regulators do not necessarily perform sufficiently well in both the normal (higher current draw) and battery backup (lower current draw) modes of operation. In the normal mode of operation, a voltage regulator should have relatively low output impedance with high current sourcing capability. In the battery backup mode of operation, the voltage regulator should have low current.
Based upon the foregoing, there is a need for an improved voltage regulator for a system having multiple power supplies.